In many technical applications, liquid is allowed to rest in basins, pools (containers) for varying lengths of time in order that particles located (suspended) in the liquid be allowed to sink to the bottom and there form a sediment. In such contexts, it is often desirable that this sediment be removed from the bottom of the container at the same time as the container is filled with liquid. For example, such needs exist in treatment plants for waste water.
It is previously known to employ for this purpose scraper devices which displace the sediment to an edge region of the bottom of the pool, normally the short side of the pool or container, which is often between 15 and 20 meters long. In order to remove the sediment which has been scraped together in this edge region, use is generally made of an arrangement comprising a pump which depends from a gantry above the pool. The pump includes a pump pipe whose intake opening is located close to the sediment strand. The pump, with its suction pipe is intended to be displaced along the strand of acculmulated sediment.
The pump equipment, with its suspension construction, is expensive and wear on the pump is extreme, since sediment of the type under contemplation here contains considerable quantities of sand. For this reason, use is often made of a simple design in which considerable quantities of air are introduced in the lower region of a "pump pipe", this air then rising upwardly in the water column inside the pump pipe. There thereby occurs a suction effect in the inlet of the pump pipe. The material in the sediment strand accompanies the water which is sucked into the pump pipe and is conveyed by the water to the outlet of the pump pipe above the surface of the water in the pool or container. This type of pump requires considerable electric power. Its lifting height above the surface of the water in the container is low. The ratio of water to sediment is very unfavourable. Normally, the sediment which is pumped up contains approximately 97% water and approximately 3% solid matter, for which reason the degree of efficiency of such an arrangement is poor in the extreme.
As disclosed above, use is also made of other more conventional pumps, but the mixture of sediment and water entails severe wear on the pumps. For all types of pumps, it applies that the mixture which is pumped up is of low total solids content and that, as a result, the mixture must be dewatered in equipment suited for this purpose, normally designated sand dewaterers.
Consequently, the art is in serious need of realizing a technique in which the degree of efficiency is considerably improved, at the same time as the operational reliability of the device itself is high and its service life long.